The invention relates to a liquid crystal display device for use as a display panel in various electronic equipment such as a timepiece (watch and clock), portable information equipment, and so forth.
A timepiece for indicating digital display of time information such as the hour, minute, and second, and calendar information such as the date, days of the week, the month, and the year, by use of a liquid crystal display panel, has been in widespread use for wrist watches and clocks, provided with a crystal oscillation circuit.
There has also been in use a combination watch wherein an analog display indicating time information by the hands of the watch is used in combination with digital display indicating time information and calendar information in numbers and letters.
Further, there has been proposed an analog watch for selectively displaying markers in various patterns, or for displaying simulated hands for an hour hand, a minute hand, and a second hand, by providing the dial thereof based on a liquid crystal display panel (refer to, for example, Japanese Patent Laid-open S 54-153066).
A reflective-type liquid crystal display device, small in size and consuming very little electric power, has been in widespread use as a display panel for displaying necessary information (character information and graphic information) in various electronic equipment other than a timepiece, such as cellular phones, desktop electronic computers, game players, and so forth.
As such a liquid crystal display device as described above, in a conventional liquid crystal display panel, a liquid crystal cell filled with liquid crystals is sandwiched between two transparent substrates having an electrode on respective inner surfaces thereof, facing each other, and an upper polarizing film and a lower polarizing film are disposed, respectively, on the external surface of the transparent substrates, on the opposite sides. If an electric field is applied to the liquid crystals by applying a voltage to a pair of electrodes on the transparent substrates holding the liquid crystal cell therebetween, the optical property of the liquid crystals is changed, thereby locally controlling transmission and absorption of light falling on the liquid crystal display panel such that a predetermined display is effected.
Either of the upper polarizing film or the lower polarizing film is a polarizing film absorbing the light linearly polarized in the direction orthogonal to the transmission axis thereof.
In the case of a watch using the conventional liquid crystal display panel described above, time information and calendar information are displayed in black against a white background in a normally white mode that is common.
However, by simply displaying time information and calendar information in black against the white background as described in the foregoing, neither variation in design nor interest can be offered, with a resulting tendency to lose soon popularity with consumers. Probably, as a result, consumption of digital watches has recently been on the decline, and neither combination watches nor analog watches with a liquid crystal display panel have since received market acceptance.
Similarly, with the conventional liquid crystal display panel used in electronic equipment other than a timepiece, various information expressed in characters and graphics is generally displayed in black against the white background, and although there are some wherein information can be displayed in white against the black background in an inverse mode, the conventional liquid crystal display panel has still been found lacking in design variation and aesthetic qualities.
In light of the present situation as described, the present invention has been developed, and an object of the invention is to provide a liquid crystal display device for use in various electronic equipment such as a timepiece (watch and clock), and so forth, capable of offering attractive variation in, design and displaying information clearly so that a viewer can see the display with greater ease.
To this end, a liquid crystal display device according to the invention comprises a liquid crystal cell with liquid crystals sealed thereinbetween, sandwiched between two transparent substrates having an electrode on each of the inner surfaces thereof facing each other, an only absorption-type polarizing film disposed on a visible side of the liquid crystal cell for a polarizing film, and an only reflection-type polarizing film disposed on a side of the liquid crystal cell, opposite from the visible side thereof for a polarizing film, and is characterized in that the absorption-type polarizing film is a polarizing sheet absorbing the light linearly polarized in the direction orthogonal to the transmission axis thereof while the reflection-type polarizing film is a polarizing sheet reflecting the light linearly polarized in the direction orthogonal to the transmission axis thereof.
With the liquid crystal display device described above, a light reflection film is preferably disposed on a side of the reflection-type polarizing film, opposite from the liquid crystal cell.
Or a color filter may be disposed on a side of the reflection-type polarizing film, opposite from the liquid crystal cell.
A light reflection film may be further disposed on a side of the color film, opposite from the reflection-type polarizing film.
Furthermore, with the liquid crystal display device described above, a light diffusing layer or light diffusing film is preferably disposed on a visible side of the absorption-type polarizing film.
For the color filter described above, any of an absorption-type color polarizing film, a dielectric multi-layered film, or an absorption-type color filter is preferably adopted.
Further, it is desirable that, with respect to the liquid crystal display devices described in the foregoing, the absorption-type polarizing film and the reflection-type polarizing film are disposed such that the transmission axes thereof either cross each other at right angles, or run in parallel with each other.
It is desirable that liquid crystals causing linearly polarized light passing therethrough to undergo phase modulation or intensity modulation are sealed in the liquid crystal cell. For such the liquid crystals, twisted nematic liquid crystals, supertwisted nematic liquid crystals, or guest-host liquid crystals are preferably used.
Furthermore, it is desirable that the absorption-type polarizing film is disposed such that the transmission axis thereof is oriented in the direction parallel with or orthogonal to the long axes of liquid crystal molecules located on a visible side of the liquid crystal cell.
With the liquid crystal display device according to the invention, constructed as described above, half of incoming light falling thereon from the visible side of the liquid crystal cell is absorbed by the absorption-type polarizing film but the other half of the incoming light is transmitted therethrough, falling on the liquid crystal cell, and when transmitted through they, liquid crystal cell, transmitted light is caused to undergo a change in optical property thereof, thereby forming portions of the liquid crystal cell where light is fully reflected by the reflection-type polarizing film, and other portions thereof where light is transmitted therethrough, so that metallic display can be effected.
Depending on whether the transmission axes of the absorption-type polarizing film and the reflection-type polarizing film, disposed on either side of the liquid crystal cell cross each other at right angles or run in parallel with each other, on whether the transmission axis of the absorption-type polarizing film is oriented in the direction parallel with or orthogonal to the direction of the long axes of the liquid crystal molecules located on the visible side of the liquid crystal cell, or depending on types of liquid crystals in use and the method of applying a voltage, either of the background part or the display segment of the liquid crystal cell can be displayed in a metallic color through full reflection of incoming light while the other can be displayed in a dark color, a color of the interior of an electronic equipment, a color reflected by the light reflection film disposed thereunder, or a color transmitted through the color filter.
By way of example, operation is described hereinafter in the case wherein the absorption-type polarizing film and the reflection-type polarizing film disposed above and below the liquid crystal cell, respectively, are arranged such that the transmission axes thereof run in parallel with each other, and the liquid crystal cell with twisted nematic liquid crystals having a twist angle of 90 degrees sealed therein is used.
Half of the incoming light from the visible side (above) of the liquid crystal cell is absorbed by the absorption-type polarizing film. The other half of the incoming light falls on the liquid crystal cell, and is transmitted therethrough. In the background part where no voltage is applied to the liquid crystals of the liquid crystal cell, transmitted light is rotated by 90 degrees, and turned into the light linearly polarized in the direction orthogonal to the transmission axis of the reflection-type polarizing film, thereby being reflected substantially in fill by the reflection-type polarizing film. As a result, the background part is displayed in a metallic color (as against a mirror).
On the other hand, in the display segment of the liquid crystal cell for displaying various information such as time information, calendar information, and so forth, where a voltage is applied to the liquid crystals, light transmitted through the liquid crystal cell is not rotated, and is turned into the light linearly polarized in the direction parallel with the direction of transmission axis of the reflection-type polarizing film, thereby being allowed to pass through the reflection-type polarizing film. Consequently, the display segment is displayed in a dark color, or can be displayed in a transparent state so as to show the internal structure of an electronic equipment in which the liquid crystal display device is mounted. Otherwise, if the light reflection film or the color filter is disposed on the underside of the reflection-type polarizing film, the display segment can be displayed in an optional color such as a color reflected by the light reflection film, or a color transmitted through the color filter.
Hence, the invention can provide a liquid crystal display device having variation in design and offering users a sense of amusement.
Furthermore, with the liquid crystal display device of the invention described above, if a light diffusing film or a light diffusing layer is disposed on the visible side of the absorption-type polarizing film, this will cause light reflected by the reflection-type polarizing film to be diffused, thereby turning display in a metallic tone into display in whiter and softer tones so as to be seen by a user with greater ease while improving a viewing angle characteristic of the liquid crystal display panel as well.